bed cap/topper vs. MPG

[LCAM-01XA]

What are your experiences - does a fullsize Ford truck cruising at 60 mph on the interstate for hours and hours on end get better fuel economy with or without a bed cap? We have a mini-convoy of two F350s: one is a 2wd IDI dually, and the other is a 4x4 big-block SRW. Both trucks are factory ride height, none lifted or lowered. 235/85-16E tires on both, all-terrain tread. IDI has a high-rise bed cap/topper, the gasser has a flat-top one - at the rear edge of the cap/topper roof they're both about 7ft tall. Should both trucks have the caps on to maximize fuel economy? Or neither? One with a cap and one without? Both truck owners have the attention span of monkeys and cannot recall past results from long road trips, so your suggestions are greatly appreciated! Thanks!

 

[93cc7.3]

i have had 3 trucks with flat covers on them all have gotten close to 3 mpgs better than with an open bed two trucks were long beds

 

[LCAM-01XA]

Sorry should have made this more clear - these are the full-height bed caps, the kind that have windows and sometimes even mosquito nets so you can go camping in them. Neither truck is equipped with a flat tonneu cover, they got refueling tanks and stuff sticking above the bed rails so a flat cover is not even an option at this point...

 

[93cc7.3]

lol sorry as well i should have elobrated a full top cover should net you more mpg than a flat cover .... if you want enough data to make your head explode check out www.ecomodders.com

 

[lindstromjd]

From what I've heard, the totally flat camper tops can actually hurt your fuel mileage. The raised tops can raise it as much as 1.5-2 mpg's. That's just going off other people talking. I have a raised cap on my PSD, and see 15-16 mpg's. The father-in-law has a flat cap on his PSD, and says he sees 17-18 with it on. Both our trucks are CC, LWB, DRW trucks with 4.10 rears.

I do know from my own experience that an open bed with an open tailgate gets you the worst fuel mileage. An open bed with a closed tailgate gets a little better (physics with air movement and all that). A tonneau cover can get you as much as 2-3 better, and truck caps are open for experimentation. It can't possibly hurt anything to see what kind of improvement you get if you throw your caps on and go through a few tanks.

 

[tanman_2006]

My mom used to swap between camper shells and tonneau covers. Her trucks with campers did worse by a couple mpg. They were all ccsb 2wd 4.6l trucks

 

[LCAM-01XA]

So your mom's trucks liked the tonneau covers more than the full caps? For us it's either full caps or nothing, we don't have the option for tonneau covers. Too bad we don't have the skills or means to build some slant-back setups (like many HMMWVs have), theoretically those should be the best...

 

[MIDNIGHT RIDER]

Myself, I would hook the goose-neck to the diesel, then load the gas-burner with the topper of choice on the goose-neck.

Whoever owns the hauled truck could pay for the fuel and everyone comes out a winner.

In the event of a catastrophic emergency, swap places and carry on.

 

[jhnlennon]

On every truck Ive ever owned, a topper DECREASED mileage. I track fuel mileage on every trip I make RELIGIOUSLY and always noticed a decrease in fuel economy with a topper on.

 

[460mudsports]

Never had a topper or a bed cover, but an 1000+ mile test did show that tailgate up got an average of 1.5 mpg better than down on our 91 ext cab longbed F250 7.3 E4OD 4.10 2wd. This truck averaged 18-20 mpg on the highway from new until it got up to 125k to 150k, then it slowly went down to about 17 by the time it was sold in 98 with 206k. It never had the injectors or pump touched, and I attribe the mileage loss to them needing replacement.

Which type of topper will help the most is purely a function of wind dynamic movement and flow over and around the truck. This is different for reg cabs vs ext cabs vs CC and short bed vs long bed. Different body styles, even hood shape i.e. 80-86 vs bricknose vs obs, make differences too. The newer you go in bodystyle, the more aerodynamics are involved in the orginal design to help maximize fuel economy. Look at how much more the windshields are laid back in the 98+ trucks compared to ours.

 

[tanman_2006]

So your mom's trucks liked the tonneau covers more than the full caps? For us it's either full caps or nothing, we don't have the option for tonneau covers. Too bad we don't have the skills or means to build some slant-back setups (like many HMMWVs have), theoretically those should be the best...

Imo it was possibly the extra weight of the camper. On highway she saw only 1-2 mpg less than the tonneau but in dd driving it was like a tank and guzzled. The parents live 15 miles from town and she makes the drive daily as a school teacher.

 

[IDIDieselJohn]

Interesting thread.


Makes me wonder how many mpg's I killed with my big old camper cap on my F150.

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Never drove the truck without that cap on it, so I have no idea.